1. Field of the Invention
The present invention relates to an AC generator for vehicles loaded on cars, trucks and the like.
2. Description of the Related Art
Recently, engine and the whole electric appliances of a vehicle are close to the road surface due to the slant nose of the vehicle. The slanted nose is designed for reducing the vehicle running resistance and improving the visibility. The water-splashing conditions caused by splashing water from tires during the running of the vehicle can be harsh. Further, in cold areas, a large amount of salts are scattered for the purpose of preventing the road from freezing during winter, and salt or water containing salt are dragged in during the running of the vehicle, resulting in harsher corrosive environment. Since the vehicular generator is exposed to the above-described environment, the generation of electrical energy may be stopped. As a result, when the vehicle stops, there is a danger of leaving people freezing to death in the cold weather.
The stoppage of the generation, in this case, is mainly caused by the fact that water is moved into the inner wall portion of the slot of the stator core thereby resulting in rust. The rust grows to reduce a sectional area of the slot, which changes after passage of time by which the conductors of the stator coil inserted into the slot is pressed to produce a short-circuit between the coils, resulting in a breakage of coil due to the burn loss of local heat generation. Further, even if insulating paper is provided to insulate between the slot and the coil, the insulating paper is sometimes broken due to the growth of rust and the rise in pressure of slot, resulting in a short-circuit between the electric conductors and stator. Furthermore, the movement of water into the slot of the coil in the slot is repeated whereby the coil film leads to corrosion deterioration such as hydrolysis. This results in a short-circuit between the electric conductors. The repeated entry of water into the slot of the coil also leads to burn loss of local heat generation and the elution of copper, finally resulting in a breakage of coil. This tendency is particularly problematic in the slot in which electric conductors of the coils are thickly present because during the step of inserting or after inserting the electric conductors into the slot of the stator coil, the insulating films on the surface of the electric conductors rub together to damage or locally reduce its thickness.
Further, in order to prevent the electric conductors of the coils, which are inserted into the slots, from projecting from the inlet of the slots, wedges made of insulating material are inserted between the electric conductors and the inlets of the slots. However, the insulation coating of the electric conductors may be harmed or thinned when inserting the wedges. Thus, in order to improve the durability, the protection of the surface of the insulation coating of the electric conductors while the stator is manufactured is very important.
In general, the coil ends are impregnated with thermosetting resin for insulation. The viscosity thereof is arranged to stay in the portions during the thermosetting period, and the resin does not flow into the slots. This does not insulate inner portions of the slots sufficiently to prevent the short circuit.
On the other hand, a slot of a stator coil can be coated with an insulating resin by means of electrode position coating or the like, and providing insulation paper for insulating between the slot and electric conductors of the coil is provided, as described in Japanese Patent Application Laid-Open No. Hei 1-278242. Further, a drip-proof cover is provided on the cooling air take-in side of a generator to cut off a direct water-splashing path from the outside, as described in Japanese Patent Application Laid-Open No. Hei 3-235644.
The method disclosed in Japanese Patent Application Laid-Open No. Hei 1-278242 provides no solution against the short-circuit between the electric conductors of coils due to the corrosion deterioration of the coil film in the slot. Further, the slot is narrowed by the thickness of the resin film and insulating paper to reduce the space for inserting the electric conductors of the coil by their thicknesses. This prohibits the increase of the thickness of the film of the coil to enhance its corrosion resistance. Since the coating step is necessary, the production cost including material cost increases.
Further, in its method disclosed in Japanese Patent Application Laid-Open No. Hei 3-235644, teaches that in a recent small and high-output vehicular generator, a fan is provided on the side of a rotor. The rotation of the fan causes cooling air is taken into the generator. A stator coil is cooled by utilizing air discharged through a window provided diametrically of a frame, as shown in FIG. 10. That is, since the stator coil is positioned near the window for ventilation provided diametrically of the frame, water or salt water from the diametrical outside of the generator can easily reach the periphery of the stator. To prevent this, it is contemplated that a drip-proof cover is further mounted externally of the window provided diametrically of the frame. In this case, however, the ventilation resistance increases and the quantity of cooling air reduces, and an escape of hot air is impeded, thus posing a problem in that a temperature of the whole generator considerably rises. This addition of the drip-proof cover increases the production cost, similarly to the addition of the coating step as described above.
Further, JP-A-63-194543 discloses an electric conductor as shown in FIG. 11. The slots are generally rectangular in cross-section. The electric conductor has a portion inserted in a slot which generally has a generally rectangular cross section and a portion outside the slot which generally has a round cross-section. Thus, occupation ratio of the electric conductor in the slot becomes more than 80%. In other words, the ratio of the area in the gap is less than 20%. However, in this structure, a number of round conductors are stacked and formed to be rectangular. Therefore, the insulation coatings are harmed or thinned due to rubbing or the difference in the degree of deformation.
The present invention solves the above-described problems of prior art. An object of the present invention is to provide an AC generator for vehicles capable of preventing stoppage of the generator due to a short-circuit within a stator slot caused by water-splashing from outside and which is excellent in terms of cost and does not pose new problem such as a rise in temperature or harm of the insulation coating of the electric conductors of the stator coil.